Process for the reaction of a low-molecular hydroxyl compound with a carboxylic acid halide

ABSTRACT

In a process for reacting a low molecular weight hydroxy compound with a carboxylic acid halide, a small amount of the acid halide is introduced into the reaction vessel and the remainder of the acid halide and the hydroxy compound are added gradually in an approximately stoichiometric ratio. The hydrogen halide formed is thus prevented from dissolving in the reaction medium. The heat of reaction to be dissipated is negligible.

The invention relates to a process for the environmentally friendlyreaction of a low-molecular hydroxyl compound with an aliphaticcarboxylic acid halide, especially of alcohols with acid chlorides.

In the preparation of esters from acid chlorides and hydroxyl compounds,the alcohol component is conventionally introduced into the reactionvessel first and the acid chloride is metered in according to thepermissible temperature and pressure relationships. HCl gas is producedin this procedure and initially dissolves in the alcohol component withthe evolution of heat. HCl gas is not released until saturation has beenreached. The advantage of this procedure is that an uncontrollablereaction of the acid chloride with undesired hydroxyl compounds, forexample water in the event of a condenser fracture, can be excluded. Theessential disadvantage of this procedure is that the HCl gas formed inthe reaction is absorbed in the alcohol initially introduced, with theevolution of a substantial heat of solution, and undergoes undesiredsecondary reactions with the alcohol component. In the case of thepreparation of methyl dichloroacetate from methanol initially introducedand dichloroacetyl chloride metered in, methyl chloride and water areformed in a temperature-dependent secondary reaction. At a temperatureof only a little above 40° C., considerable amounts of methyl chlorideare formed, which is undesired on account of its polluting properties.Methyl chloride can even be detected in the released HCl gas in thetemperature region below 40° C., creating the need for a specialpurification of the effluent gas.

In the working-up of such a reaction mixture, especially in the presenceof readily saponifiable esters such as e.g. methyl dichloroacetate, thewater which is also formed in this secondary reaction results in anundesired saponification, i.e. in a possibly substantial reduction ofthe ester yield.

It has now been found that the above-described disadvantages in thepreparation of esters from acid halides and low-molecular hydroxylcompounds can be avoided by a procedure in which the acid halide isinitially introduced and the hydroxyl compound is metered in.

The invention thus relates to the process described in the claims.

In the process according to the invention, low-molecular hydroxylcompounds are reacted with acid halides. Suitable hydroxyl compounds arewater, aliphatic C₁ -C₁₂ alcohols, cycloaliphatic C₆ -C₁₂ alcohols andaromatic alcohols. It is preferred to use water, aliphatic C₁ -C₁₂alcohols and cycloaliphatic C₆ -C₁₂ alcohols, especially water andaliphatic C₁ -C₄ alcohols, for example methanol, ethanol, n- andi-propanol and butanols.

Suitable carboxylic acid halides are the fluorides, chlorides andbromides, preferably bromides and chlorides, of aliphatic C₂ -C₆carboxylic acids, cycloaliphatic C₆ -C₁₂ carboxylic acids and aromaticcarboxylic acids. It is preferred to use the chlorides of loweraliphatic C₂ -C₆ halogenocarboxylic acids such as, for example,chloroacetic acids or chloropropionic acids.

The reactants are reacted in such a way that the carboxylic acid halideis maintained in excess during the reaction and the hydroxyl compound isadded to the acid halide. For this purpose, 5 to 20 mol % of the totalamount of acid halide intended for the reaction is initially introducedinto the reaction vessel and the remaining acid halide and the hydroxylcompound are then introduced gradually, in approximately stoichiometricproportions, at a rate which depends on the removal of the hydrogenhalide and the heat of reaction. At the end, when the amount of acidhalide to be added has been consumed, the acid halide remaining in thereaction vessel is also reacted. The hydroxyl compound is introducedinto the reaction vessel in an amount of 105 to 120 mol % based on thetotal acid halide.

If the reactants are liquid, they are preferably brought together inundiluted form in the absence of a solvent. Solid reactants areconveniently dissolved before the reaction in an inert solvent, forexample in an aliphatic, cycloaliphatic or aromatic hydrocarbon, incarbon tetrachloride or in other inert halogenated hydrocarbons, forexample in trichloroethene.

The reaction temperature depends on the pressure and the reactants andis 20 to 100 and preferably 20° to 50° C. or, in the case where acidchlorides are reacted, up to 40° C. The pressure is 1 to 3 andpreferably 1 to 1.5 bar.

Any apparatus suitable for esterification reactions can be used as thereaction vessel, for example flasks and kettles equipped with stirrers,reflux condenser, feed vessels and monitoring and control devices.

The reaction product formed, namely acid or ester, is obtained in pureform by generally known methods such as distillation, crystallization orsome other process. In some cases, the reaction product can be usedwithout a further purification operation.

The process according to the invention produces practically no heat ofsolution needing to be removed, because the hydrogen halide formed bythe reaction is only slightly soluble in the acid halide. The hydrogenhalide is released right from the beginning of the reaction. Acids whichare not readily accessible by other methods can also be obtained by thisprocess in good yield from their acid chlorides.

Where glass apparatuses are used, a possible fracture of the refluxcondenser and penetration of cooling water into the reaction space doesnot cause a runaway reaction.

The following Examples will serve to illustrate the invention.

Example 1 Preparation of ethyl dichloroacetate (EDA)

500 cm³ of dichloroacetyl chloride (DAC) (corresponding to 766.5 g=5.20mol) were reacted with 319 cm³ of absolute ethanol (corresponding to251.7 g=5.46 mol) in a 2 dm³ 4-necked flask equipped with an internalthermometer, a high-efficiency condenser, a stirrer, a Claisenattachment and two 500 cm³ dropping funnels. To perform the reaction, 10cm³ of DAC were initially introduced into the flask, with the stirrerrunning, and DAC and ethanol were continuously added dropwise from boththe dropping funnels, DAC being maintained in excess up to the end ofthe reaction. The rate of dropwise addition was regulated so that every10 cm³ of DAC reacted with 6.1 cm³ of ethanol in approximatelystoichiometric proportions in about 1.5 minutes. During the reaction,the mixture was cooled so as to prevent the internal temperature fromexceeding 40° C. The HCl gas produced in the reaction was removed viathe high-efficiency condenser.

Towards the end of the reaction, when all the DAC had been run in, theother dropping funnel still contained ca. 18-24 cm³ of ethanol, whichwas introduced into the flask in a molar excess of 5% in order toconvert the excess DAC.

During the reaction itself, the addition of DAC and ethanol had to bemonitored continuously, the amount of ethanol metered in being allowedto vary only by at most ±3 cm³ relative to the predetermined value. Inpractice, this means that, over the same periods of time, the amount ofethanol added corresponded to about 55-60% of the amount of DAC whichcould be read off on the dropping funnels.

When the reaction had ended, the mixture was stirred for about a further1/4 hour to complete the conversion and to remove the HCl gas. The ethyldichloroacetate formed was then purified by vacuum distillation. 778 gof EDA were obtained after vacuum distillation, this being a yield of95.3% based on DAC.

Example 2 Preparation of ethyl trichloroacetate (ETA)

Ethyl trichloroacetate (ETA) was also prepared in the same apparatus,analogously to the preparation of ethyl dichloroacetate.

For this purpose, 500 cm³ of trichloroacetyl chloride (TAC)(corresponding to 812.5 g=4.47 mol) were reacted with 274 cm³ ofabsolute ethanol (corresponding to 216.3 g=4.69 mol). The reaction wasagain carried out by a procedure in which 10 cm³ of TAC were initiallyintroduced into the reaction vessel and maintained in excess up to theend of the reaction. TAC and ethanol were continuously added dropwisefrom both the dropping funnels, every 10 cm³ of TAC reacting with 5.2cm³ of ethanol in approximately stoichiometric proportions. The amountof ethanol metered in was allowed to vary only by at most ±2.5 cm³relative to the predetermined value.

During the reaction, the mixture was cooled and the HCl gas was removedvia the high-efficiency condenser.

When all the TAC had been run in, the ethanol dropping funnel stillcontained ca. 16-21 cm³ of ethanol, which was added in excess in orderto convert the excess TAC.

When the reaction had ended, the mixture was stirred for about a further1/4 hour. The ethyl trichloroacetate was then purified by vacuumdistillation.

778 g of ETA were obtained, this being a yield of 91% based on TAC.

Example 3 Preparation of n-butyl trichloroacetate (BTA)

Butyl trichloroacetate was prepared analogously to Example 1. 500 cm³TAC (812.5 g, corresponding to 4.47 mol) were reacted with 429.4 cm³ ofn-butanol (347.8 g, corresponding to 4.69 mol) in the apparatusdescribed. The reaction was again carried out by a procedure in which 10cm³ of TAC were initially introduced into the reaction vessel and 10 cm³of TAC and 8.2 cm³ of n-butanol were metered in over the same periods oftime. The amount of butanol metered in was allowed to vary only by atmost ±4 cm³ relative to the predetermined value.

When the reaction had ended, the remaining n-butanol, i.e. 25-33 cm³,was added, the mixture was stirred for a quarter of an hour and theester formed was distilled under vacuum. The yield was 915 g of BTA,i.e. 93.3% based on TAC.

Example 4 Preparation of methyl dichloroacetate (MDA)

2590 dm³ of DAC (corresponding to 4000 kg=27.14 kmol) were reacted with1150 dm³ of methanol (corresponding to 910 kg=28.4 kmol) in a 4 m³stirred kettle.

For this purpose, 30 dm³ of DAC were initially introduced into thestirred kettle, with the stirrer running, and methanol and DAC were thenmetered in, in stoichiometric proportions, by means of two meteringpumps driven by one motor via a common drive shaft.

The reactants were introduced via meters and rotameters. The meteringoperation was carried out in such a way that 17 dm³ of methanol weremetered in over the same period of time in which 40 dm³ of DAC wereinjected. These amounts were set at the metering pumps and continuouslymonitored. The amount of methanol metered in was allowed to vary only byat most ±8 dm³ relative to the predetermined aggregate desired value. Inthis process, the methanol reacted with the DAC to give MDA with aslightly exothermic heat tonality. The heat of reaction was removed bymeans of jacket cooling. The temperature did not exceed 40° C.

As ca. 30 dm³ of DAC were present in excess in the reactor throughoutthe entire reaction, there was a vigorous production of HCl gas rightfrom the start. In the present case, the stirred kettle was providedwith a column and attached glass condensers through which the HCl gaswas released. Any entrained product was retained in the condensers anddripped back into the reaction vessel. For safety reasons, the unit wasoperated in such a way that the pressure of HCl gas in the unit did notexceed 1.2 bar. After about 7.5 hours, the total amount of DAC of 2590dm³ (including the 30 dm³ initially introduced) DAC [sic] had reactedwith 1100 dm³ of methanol. This point was signalled by a cessation ofHCl production and a drop in the pressure in the unit. To complete thereaction, a further 50 dm³ of methanol were then metered in and thewhole mixture was stirred for 15 minutes.

The reaction mixture was subsequently distilled under vacuum to give3650 kg of MDA, this being a yield of 94.3% based on DAC.

Example 5 Preparation of dichloroacetic acid (DAA)

Analogously to the preparation of MDA, 2590 dm³ of DAC (corresponding to4000 kg=27.14 kmol) were reacted with 540 dm³ of water (540 kg=30 kmol)in the same 4 m³ stirred kettle.

For this purpose, 30 dm³ of DAC were again introduced initially into thestirred kettle. The remaining DAC was then metered in with the water instoichiometric proportions.

The reactants were introduced analogously via meters and rotameters. Themetering operation was carried out in such a way that 7.5 dm³ of waterwere injected over the same period of time in which 40 dm³ of DAC weremetered in. The amount of water metered in was allowed to vary by atmost ±3 dm³ relative to the predetermined aggregate desired value; itwas continuously checked. The DAC excess of 30 dm³ was maintained up tothe end of the reaction. After ca. 7 hours, the total amount of DAC of2510 dm³ (including the 30 dm³ initially introduced) had reacted with490 dm³ of water. To complete the reaction, a further 50 dm³ of waterwere then metered in and the mixture was stirred for 15 minutes.Subsequent vacuum distillation gave 3390 kg of dichloroacetic acid, thisbeing a yield of 96.8% based on DAC.

What is claimed is:
 1. A process for the preparation of a carboxylic acid or carboxylic acid ester by reacting, in a reaction zone, a hydroxyl compound and a carboxylic acid halide, comprising the steps of:introducing into the reaction zone 5 to 20 mol % of the total amount of carboxylic acid halide to be reacted, introducing into the reaction zone over a period of time the remainder of said total amount of carboxylic acid halide while introducing into the reaction zone a first amount of hydroxyl compound, said first amount of hydroxyl compound being approximately stoichiometric with respect to said remainder, the rate of introduction of said first amount of hydroxyl compound being approximately stoichiometric with respect to the rate of introduction of said remainder, so that during and at the conclusion of the introduction of said first amount of hydroxyl compound, essentially unreacted carboxylic acid halide is present in the reaction zone, adding a second amount of hydroxyl compound which is at least stoichiometric with respect to said essentially unreacted carboxylic acid halide present in the reaction zone at the conclusion of the introduction of said first amount of hydroxyl compound, the total of said first amount and said second amount of hydroxyl compound being 105 to 120 mol %, based on said total amount of carboxylic acid to be reacted.
 2. A process as claimed in claim 1, wherein the hydroxyl compound comprises water, in which case the product formed in the reaction zone comprises a carboxylic acid, or a C₁ -C₁₂ -alcohol, in which case the product formed in the reaction zone comprises a carboxylic acid ester.
 3. A process as claimed in claim 2, wherein the hydroxyl compound comprises water, and a carboxylic acid is recovered from the reaction zone as the product of the process.
 4. A process as claimed in claim 2, wherein the hydroxyl compound comprises an aliphatic C₁ -C₁₂ -alcohol, and a carboxylic acid ester is recovered from the reaction zone as the product of the process.
 5. A process as claimed in claim 1, wherein the hydrogen halide formed as a byproduct of the reaction of the carboxylic acid halide and the hydroxyl compound is released from the reaction zone at the beginning and during said reaction, due to the low solubility of the hydrogen halide in carboxylic acid halide.
 6. A process as claimed in claim 1, wherein the carboxylic acid halide is a chloride of an aliphatic C₂ -C₆ -halogenocarboxylic acid.
 7. A process as claimed in claim 1, wherein the carboxylic acid halide and the hydroxyl compound are both liquids and are reacted in the reaction zone essentially in the absence of a solvent.
 8. A process for the preparation of a halogenocarboxylic acid or a halogenocarboxylic acid ester by reacting, in a reaction zone, halogenocarboxylic acid chloride with water or a C₁ -C₁₂ -alcohol, comprising the steps of:first introducing into the reaction zone 5 to 20 mol % of the total amount of halogenocarboxylic acid halide to be reacted, then metering into the reaction zone over a period of time the remainder of said total amount of halogenocarboxylic acid halide, while, over essentially the same period of time, metering into the reaction zone a first amount of water or said alcohol, said first amount of water or said alcohol being approximately stoichiometric with respect to said remainder, the rate of metering of said first amount of water or said alcohol being substantially the same, on a molar basis, as the rate of metering of said remainder, so that during and at the conclusion of the metering-in of said first amount of water or said alcohol, at least about 5 mol % of essentially unreacted halogenocarboxylic acid halide, with respect to said total amount of carboxylic acid halide to be reacted, remain in the reaction zone, throughout this metering step, removing hydrogen chloride from the reaction zone, adding a second amount of water or said alcohol which is in excess over stoichiometry with respect to said essentially unreacted halogenocarboxylic acid halide remaining in the reaction zone, the total of said first amount and said second amount of water or said alcohol being 105 to 120 mol %, based on said total amount of halogenocarboxylic acid, and recovering the resulting halogenocarboxylic acid or halogenocarboxylic acid ester from the reaction zone as the product of the process. 